The present invention relates generally to compositions and methods for repairing superalloys, and more particularly to compositions and methods for the braze repair of nickel- and/or cobalt-based superalloy parts.
Nickel- and/or cobalt-based superalloys are commonly used by the aerospace and power industries for components such as turbine vanes that will be subjected to high temperatures and stress. While such alloys are inherently strong and resistant to damage, cracks and ruptures occasionally occur. When the damage is relatively minor, repairs can be made, such as, for example, by braze repair.
High temperature diffusion braze technology is normally used to repair turbine vanes made of Ni- and Co-based superalloys. The braze alloy mixture typically includes two powdered constituents. The first constituent (the base metal powder) is a high temperature powder with a chemistry the same as, or similar to, the component being repaired. The second constituent (the braze alloy powder) consists of a high temperature diffusion braze alloy that has a melting temperature well below that of the base metal powder. This braze alloy powder is used to join the base metal powder particles together, and to join the composite powder mixture to the areas of the component being repaired.
Diffusion braze alloy powders typically contain melting point depressants such as boron and/or silicon of elements. Unfortunately though, the use of boron and silicon in braze alloys can have a negative impact on the mechanical and/or environmental properties of the repaired area of the part. In particular, large, blocky or script-like brittle phases are formed which decrease the ability of the material to resist rupture from stress. These brittle phases are composed of refractory elements, chromium, and/or titanium combined with boron, silicon and carbon. For the braze repair of directional solidified (DS) superalloys with columnar-grained (CG) and single-crystal (SC) microstructure, B and Si are particularly detrimental to the mechanical properties and oxidation resistance.
A need therefore exists for improved braze repair alloy powders with minimal amounts of B and/or Si, that can be used for repairing superalloys such as those found in jet engine turbine vanes. The present invention addresses that need.
Briefly describing one aspect of the present invention, there is provided a braze alloy powder mixture comprising a low-melt powder composition and a high-melt powder composition. The low-melt powder composition may be made from a single low-melt alloy powder, or it may be a mixture of more than one low-melt alloy powder. In either event, the low-melt powder composition preferably comprises, by weight, 50-70% Ni, 8-20% Cr, 8-15% Ta, 4-10% Co, 2-7% Al, and up to about 2.25% B. Similarly, the high-melt powder composition may be made from a single high-melt alloy powder, or it may be a mixture of more than one high-melt alloy powder. In either event, the high-melt powder composition preferably comprises, by weight, 50-70% Ni, 2-10% Cr, 2-10% Ta, 5-15% Co, 2-10% Al, 2-10% W, and up to about 3% each Re, Mo and/or Hf.
In the most preferred embodiments the low-melt powder composition also comprises up to about 1% each of any or all of the following: Ti, W, Mo, Re, Nb, Hf, Pd, Pt, Ir, Ru, C, Si, and Zr, and the high-melt powder composition also comprises up to about 1% each of any or all of the following: Ti, Nb, C, B, Si, and Zr.
Accordingly, the braze alloy mixture (that is, the combination of low-melt and high-melt powders) preferably comprises 50-70% Ni, 10-15% Cr, 8-10% Ta, 8-10% Co, 4-7% Al, 2-4% W, about 1-2% Re, and about 0.5-1% each of Mo and Hf. In the most preferred embodiments the braze alloy mixture also comprises up to about 1% each of any or all of the following: Ti, Nb, Pd, Pt, Ir, Ru, C, B, Si, and Zr.
One object of the present invention is to provide braze alloy powders useful for the braze repair of Ni- and/or Co-based superalloys.
Other objects and advantages will be apparent from the following description.